The present invention relates to a coating head for coating various kinds of materials such as a resist, and a coloring sensitive material on a substrate in a production process of a semiconductor, a liquid crystal display device, a color filter, or the like.
Conventional coating heads have adopted a coating method by extruding a pressured liquid from a certain liquid ejecting slit as found in a dye coat head, a curtain coat head, or the like. FIG. 4(A) is an entire perspective view of conventional coating head and substrate, FIG. 4(B) is a cross-sectional view of the central part in the longitudinal direction of the coating head of FIG. 4(A) taken on the plane parallel with the paper surface, FIG. 4(C) is a cross-sectional view taken along the line Cxe2x80x94C of FIG. 4(B), and FIG. 4(D) is a diagram for explaining the coating state.
In FIG. 4(A), a coating head 2 is provided on the lower surface of a substrate 1 such that the substrate 1 and the coating head 2 are moved relatively in the arrow P direction in the figure. A coating liquid supply tube 3 is mounted on the coating head 2.
As shown in FIGS. 4(B) and 4(C), the coating head 2 comprises a liquid supply opening 5 formed in the lower center part, a first chamber 6 communicating with the liquid supply opening 5, a second chamber 7 communicating with the first chamber 6, narrower than the first chamber 6, and a liquid ejecting slit 8 communicating with the second chamber 7, further narrower than the second chamber 7. Furthermore, the lower surface and the upper surface of the first chamber 6 are provided as parallel inclined surfaces 6a and 6b tilted from the liquid supply opening 5 upward to right and left sides, and the upper surface of the second chamber 7 is provided as a horizontal surface 7a. 
In the coating head 2 with the above-mentioned configuration, a coating liquid from the liquid supply opening 5 is extruded from the liquid ejecting slit 8 via the first chamber 6 and the second chamber 7. At the time, the lower surface and the upper surface of the first chamber 6 are provided as the inclined surfaces 6a and 6b, the upper surface of the second chamber 7 is provided as the horizontal surface 7a, and the first chamber 6, the second chamber 7, and the liquid ejecting slit 8 are formed so as to be narrower successively. Therefore, the pressure loss of the coating liquid can be homogeneous from the liquid supply opening 5 to the right and left entire surface of the liquid ejecting slit 8, and thus the coating liquid can be extruded homogeneously from the entire surface of the liquid ejecting slit 8 as shown by the arrows in FIG. 4(B).
According to the above-mentioned conventional coating head, the first and second chambers 6 and 7 are designed and produced so as to have the optimum shape in view of the coating liquid viscosity, the rheology characteristic, the supply rate (flow amount), or the like in order to extrude the coating liquid homogeneously from the entire surface of the liquid ejecting slit 8.
However, a highly sophisticated process of the inclined surfaces 6a and 6b of the first chamber 6, the horizontal surface 7a of the second chamber 7 and the liquid ejecting slit 8 inside the coating head 2 is limited. Moreover, a problem is involved in that common use of the coating head for different coating liquids is difficult. Furthermore, a problem is involved in that use with the optimum internal shape cannot always be realized due to fluctuation of the ejection amount, the rate, and the pressure in a process so that ejection amount non-uniformity is generated.
Moreover, in the case intermittent coating (method of coating only by a one way process at one time) using this coating head is executed, coating non-uniformity M is generated from midway to the end of coating as shown in FIG. 4(D), particularly in the case of a highly viscous material. This is because the flow is changed drastically to right and left from the supply opening Q in the central part in the case of the highly viscous material so that the flow amount in the center part is reduced.
In order to solve the above-mentioned conventional problems, an object of the present invention is to provide a coating head, capable of restraining non-uniformity and fluctuation of the ejection amount so as to improve the coating quality.
In order to achieve the object, a first aspect of the present invention is a coating head comprising a liquid supply opening formed in a bottom part of the coating head, a first chamber communicating with the liquid supply opening, tilted toward the longitudinal direction end part, a second chamber communicating with the first chamber, narrower than the first chamber, a liquid ejecting slit communicating with the second chamber, further narrower than the second chamber, and a third chamber formed halfway in the liquid ejecting slit, elongating in the horizontal direction.
Moreover, a second aspect of the present invention is a coating head comprising a liquid pool part formed in a bottom part of the coating head, a liquid ejecting slit communicating with the liquid pool part, opened to the atmosphere, and a liquid supply path formed parallel with the liquid ejecting slit with an interval, with one end communicating with the liquid supply opening and the other end communicating with the liquid pool part, wherein the liquid supply path comprises a first chamber communicating with the liquid supply opening, tilted toward the longitudinal direction end part, a second chamber communicating with the first chamber, narrower than the first chamber, and a slit with one end communicating with the second chamber and the other end communicating with the liquid pool part, further narrower than the second chamber.
According to the present invention, since a chamber is provided halfway in a liquid ejecting slit, or a liquid pool part is formed on a bottom part of a coating head, the coating amount can be ensured sufficiently as well as the pressure fluctuation can be absorbed, and thus the coating quality can be improved by restraining non-uniformity and fluctuation of the ejection amount. Moreover, according to the second aspect of the present invention, since the coating liquid paths face with each other with respect to a liquid pool part, the length of the liquid ejecting slit can be ensured sufficiently so that ejection can be enabled by extruding with little influence by the flow, and thus the coating quality can be improved by making the ejection accuracy better.